One type of food container has a container body with an interior defined by a bottom wall, an upstanding sidewall and an open upper end. The open upper end may have a neck, such as with external threading, and an upward facing rim. A tamper evident member or sealing member can be sealed to the rim to cover the open upper end of the container body and, in some circumstances, to provide a visual indication of tamper evidence. A lid can be placed over the sealing membrane, and can have a closure wall with a depending skirt. The skirt may have an internal thread for mating with the external threads of the neck of the container body.
If the sealing membrane is completely sealed to the rim, then any gasses present or generated within the interior of the container body can cause the sidewall of the container to deform. This can be particularly the case when a food container is shipped across high altitudes, such as by crossing over high mountains. In addition to deformation due to expansion, the container body can also deform inwardly if there is a reduction in pressure in the interior of the container body as compared to exterior of the container. Deformation of the container body is undesirable, and can result in containers having visually unappealing appearances. Deformation, if sufficient, can also rupture the sealing membrane from the rim, resulting in a product that can appear to have been tampered with.
To address the problems associated with deformation of the container body, in the past skip seals have been made between the sealing membrane and the rim of the container body. A skip seal is a small gap in the sealing between the sealing membrane and the rim of the container body that is configured to permit gasses to enter and leave the interior of the container body.
One way of attaching the sealing membrane to the rim of the container body is by using induction heating. In induction heating, pressure is applied on a surface of the sealing membrane urging the sealing membrane against the rim of the container body. The pressure can be applied using raised or otherwise configured portions of the lid. With pressure applied, the food container is sent through an induction heater, which causes the sealing membrane to seal to the rim of the container in areas where pressure is applied by the lid.
The pressure-applying portion of the lid is supposed to be configured to apply pressure only in certain areas, so that the sealing membrane is not sealed to the entirety of the rim of the container so that skip seals are formed. However, sealing between the sealing membrane and the rim of the container body can inadvertently occur, which can close the skip seals and result in a container body that is completely sealed by the sealing membrane. For example, if the sealing membrane has a size larger than the periphery of the rim of the container body, as is often the case, then edges of the sealing membrane can inadvertently seal to the container rim and close the intended skip seals. In this example, the lid can exert pressure on a portion of the sealing membrane extending past the rim and cause the sealing membrane to seal to the rim or adjacent to the rim, resulting in closed skip seals. Closed skip seals can lead to the undesirable deformations of the container body discussed above.